Add support for block headers of variable length, when parsing headers messages.

core/src/main/java/org/bitcoinj/core/BitcoinSerializer.java

@@ -266,8 +266,8 @@ public class BitcoinSerializer extends MessageSerializer {
      * serialization format support.
      */
     @Override
-    public Block makeBlock(final byte[] payloadBytes, final int length) throws ProtocolException {
+    public Block makeBlock(final byte[] payloadBytes, final int offset, final int length) throws ProtocolException {
-        return new Block(params, payloadBytes, this, length);
+        return new Block(params, payloadBytes, offset, this, length);
     }
 
     /**

core/src/main/java/org/bitcoinj/core/Block.java

@@ -134,6 +134,21 @@ public class Block extends Message {
         super(params, payloadBytes, 0, serializer, length);
     }
 
+    /**
+     * Construct a block object from the Bitcoin wire format.
+     * @param params NetworkParameters object.
+     * @param payloadBytes the payload to extract the block from.
+     * @param offset The location of the first payload byte within the array.
+     * @param serializer the serializer to use for this message.
+     * @param length The length of message if known.  Usually this is provided when deserializing of the wire
+     * as the length will be provided as part of the header.  If unknown then set to Message.UNKNOWN_LENGTH
+     * @throws ProtocolException
+     */
+    public Block(NetworkParameters params, byte[] payloadBytes, int offset, MessageSerializer serializer, int length)
+            throws ProtocolException {
+        super(params, payloadBytes, offset, serializer, length);
+    }
+
     /**
      * Construct a block object from the Bitcoin wire format. Used in the case of a block
      * contained within another message (i.e. for AuxPoW header).

core/src/main/java/org/bitcoinj/core/DummySerializer.java

@@ -64,7 +64,7 @@ class DummySerializer extends MessageSerializer {
     }
 
     @Override
-    public Block makeBlock(byte[] payloadBytes, int length) throws UnsupportedOperationException {
+    public Block makeBlock(byte[] payloadBytes, int offset, int length) throws UnsupportedOperationException {
         throw new UnsupportedOperationException(DEFAULT_EXCEPTION_MESSAGE);
     }
 

core/src/main/java/org/bitcoinj/core/HeadersMessage.java

@@ -64,33 +64,27 @@ public class HeadersMessage extends Message {
 
     @Override
     protected void parse() throws ProtocolException {
-        if (length == UNKNOWN_LENGTH) {
-            int saveCursor = cursor;
-            long numHeaders = readVarInt();
-            cursor = saveCursor;
-
-            // Each header has 80 bytes and one more byte for transactions number which is 00.
-            length = (Block.HEADER_SIZE + 1) * (int)numHeaders;
-        }
-
         long numHeaders = readVarInt();
         if (numHeaders > MAX_HEADERS)
             throw new ProtocolException("Too many headers: got " + numHeaders + " which is larger than " +
                                          MAX_HEADERS);
 
         blockHeaders = new ArrayList<Block>();
+        final BitcoinSerializer serializer = this.params.getSerializer(true);
 
         for (int i = 0; i < numHeaders; ++i) {
-            // Read 80 bytes of the header and one more byte for the transaction list, which is always a 00 because the
+            final Block newBlockHeader = serializer.makeBlock(payload, cursor, UNKNOWN_LENGTH);
-            // transaction list is empty.
+            if (newBlockHeader.hasTransactions()) {
-            byte[] blockHeader = readBytes(Block.HEADER_SIZE + 1);
-            if (blockHeader[Block.HEADER_SIZE] != 0)
                 throw new ProtocolException("Block header does not end with a null byte");
-            Block newBlockHeader = this.params.getSerializer(true)
+            }
-                .makeBlock(blockHeader, Block.HEADER_SIZE + 1);
+            cursor += newBlockHeader.optimalEncodingMessageSize;
             blockHeaders.add(newBlockHeader);
         }
 
+        if (length == UNKNOWN_LENGTH) {
+            length = cursor - offset;
+        }
+
         if (log.isDebugEnabled()) {
             for (int i = 0; i < numHeaders; ++i) {
                 log.debug(this.blockHeaders.get(i).toString());

core/src/main/java/org/bitcoinj/core/MessageSerializer.java

@@ -69,7 +69,15 @@ public abstract class MessageSerializer {
      * length as block length.
      */
     public final Block makeBlock(byte[] payloadBytes) throws ProtocolException {
-        return makeBlock(payloadBytes, payloadBytes.length);
+        return makeBlock(payloadBytes, 0, payloadBytes.length);
+    }
+
+    /**
+     * Make a block from the payload, using an offset of zero and the provided
+     * length as block length.
+     */
+    public final Block makeBlock(byte[] payloadBytes, int length) throws ProtocolException {
+        return makeBlock(payloadBytes, 0, length);
     }
 
     /**
@@ -77,7 +85,7 @@ public abstract class MessageSerializer {
      * length as block length. Extension point for alternative
      * serialization format support.
      */
-    public abstract Block makeBlock(byte[] payloadBytes, int length) throws ProtocolException;
+    public abstract Block makeBlock(final byte[] payloadBytes, final int offset, final int length) throws ProtocolException, UnsupportedOperationException;
 
     /**
      * Make an filter message from the payload. Extension point for alternative